The present invention relates to a device for transmitting the movement to a fan for cooling the coolant in a motor vehicle, comprising a first electromagnetic clutch, a second clutch and means for engaging/disengaging the second clutch, comprising an actuating element coaxially displaceable, in both directions, with respect to the movement generating means, but idle upon rotation thereof.
It is known in the technical sector relating to the cooling of coolants contained in motor-vehicle radiators that there is a need to force air onto the radiator in order to obtain more rapid dissipation of heat from the coolant to the exterior, the forced air flow being obtained by causing rotation of a fan which is normally mounted either directly on the crankshaft or on the water pump shaft or on a driven and fixed shaft carrying a pulley which receives movement from a belt actuated by the crankshaft.
It is also known that said fan must be made to rotate only upon reaching a certain predefined temperature of the water detected by means of a thermostat which activates an electromagnetic clutch, closing of which causes the fan to start rotating.
Said electromagnetic clutches cause the fan to start rotating at the speed of rotation of the actuating pulley, without the possibility of causing a variation in the speed of rotation of the fan depending on the variation in speed of actuation thereof.
More particularly it is required that a motor vehicle fan must be able to rotate:
at a lower speed than that of the transmission shaft for cooling in low external temperature conditions;
at a speed equal to or even greater than that of the transmission shaft in the case of higher external temperatures or use in severe conditions which cause overheating of the engine;
at zero speed, namely with the fan which does not rotate at all and remains in an idle condition with respect to the transmission shaft, in the case of particularly low temperatures at which further cooling is of no use or even damaging.
In an attempt to achieve these performance features, coupling systems of the mixed type with electromagnetically operated friction clutches and drive couplings based on the use of parasitic currents generated by rotation of a conducting element in the vicinity of permanent magnets have been developed.
This solution is, for example, known from DE 3 203 143 which describes an arrangement in which the crankshaft is connected to the rotor of an electromagnetic clutch, engaged by an armature connected to the fan for direct driving, whereas low speed conditions make use of the engagement between a conducting disk, rotating with the transmission shaft, and the permanent magnets integral with the fan, said engagement causing transmission of movement at a low speed as a result of relative slipping between the two parts.
With this solution, however, it is not possible to obtain the idle condition of the fan.
In order to overcome this drawback, EP 0 317 703 described a coupling which, adopting the solution disclosed by the preceding patent DE 3 203 143, also envisages a second electromagnetic clutch which, in combination with the others, is able to achieve the three different operating conditions, but requires the manufacture of a special bearing, which is not standard and is expensive and difficult to produce.
Both the solutions also have a structural limitation consisting in the fact that the slow speed is predetermined by the size of the permanent magnets necessary for operation of the clutch and it is therefore not possible to regulate the slow speed of rotation of the fan within a variable range corresponding to the actual temperature conditions of the engine.
In addition to this, the particular configuration of the engine compartments of motor vehicles for which said devices are intended requires, in particular in the case of a fan supported by a fixed shaft carrying the actuating pulley, the positioning of large projecting rotational masses at a considerable distance from the point of attachment of the fixed shaft supporting the fan, with obvious drawbacks resulting in the need, among other things, for brackets and fixtures for the whole assembly; this gives rise to a further increase in the dimensions, technical difficulties in configuration of the partsxe2x80x94due to the presence in the engine compartment of other engine partsxe2x80x94and a consequent overall increase in the manufacturing costs.
An object of the invention is to provide device for transmitting the rotational movement to a fan for cooling the coolant of motor vehicles, which is actuated by a single actuating means and allows the fan to rotate at a controllable number of revolutions adjustable depending on the actual cooling requirement of the engine, which also includes the possibility of keeping the fan stationary in the case of very low external temperatures.
Another object is to provide a device which has compact dimensions without high and costly projecting rotational masses and should be controlled by means of direct detection of the temperature of the coolant.
These objects are achieved according to the present invention by a device for transmitting the movement to a fan cooling the coolant of a motor vehicle, comprising movement generating means on which the fan is mounted by means of an idle support, a first electromagnetic clutch, engagement of which causes rotation of the fan at a number of revolutions equal to that of the movement generating means; a second clutch, engagement/disengagement of which causes rotation of the fan at a number of revolutions lower than that of the movement generating means or at zero revolutions; means for engaging/disengaging the second clutch comprising an actuating element coaxially displaceable, in both directions, with respect to the movement generating means, but idle upon rotation of the latter; and engaging means which are coaxially locked in rotation with the movement generating means and connected to said displacement actuating element and suitable for engagement/disengagement with the rotor of the said second clutch.